1. Field of the Invention
The present invention relates to a method of and apparatus for measuring arterial blood pressure and pulse rate.
2. Description of the Prior Art
Blood pressure levels are typically measured manually by use of a sphygmomanometer wrapped around an individual's arm. This device includes a pressure gauge and an inflatible cuff which terminates the flow of blood through an artery during the measurement process. A sphygmomanometer is incapable of providing a continuous read out of systolic and diastolic blood pressure levels.
A second type of blood pressure measurement device provides a continuous blood pressure read out and includes a pressure transducer which must be surgically implanted within an artery.
U.S. Pat. No. 2,658,505 (Sheer) discloses an arterial pulse wave velocity meter having a piezoelectric transducer which is coupled to an exteriorized artery. The transducer utilized in connection with this device generates electrical signals representative of the displacement of the artery wall and the rotational force imparted to a second element of the transducer. An electrical differentiating circuit is provided to obtain the rate of change of the displacement waveform. Additional circuitry is provided to measure the ratio between the differentiated values and the electrical signal created by torsional forces. This ratio is utilized to determine the velocity of the arterial pulse wave.
U.S. Pat. No. 3,132,643 (Baum) determines blood pressure by measuring the time lapse between an electrocardiac signal generated by the heart and a consequent pressure pulse measured at a remotely located point on the body.
U.S. Pat. No. 3,095,872 (Tolles) measures blood pressure by impressing continuous wave alternating pressure signals on a flow of arterial blood. Phase changes in the continuous wave modulation signal between two points spaced along the arterial blood stream are measured to determine relative blood pressure levels.
U.S. Pat. No. 3,734,086 (Phelps) discloses an apparatus for detecting, measuring and displaying the pulse propagation time from the heart to an extremity by non-invasive means.
U.S. Pat. No. 2,114,578 (Strauss) discloses an apparatus for visibly indicating the frequency and amplitude of the human pulse. A rubber compression bag is used in combination with a piezoelectric crystal to convert blood pressure pulsations into electrical impulses.